POLYPHOSPHATE DERIVATIVE OF A 1,3,5-TRIAZINE COMPOUND, A PROCESS FOR THE PRODUCTION THEREOF

Abstract

A polyphosphate derivative of a 1, 3, 5-triazine compound, preferably melamine polyphosphate, with a) an average condensation coefficient n (number average) > 20, b) with a pH-value of a 10% slurry of the polyphosphate derivative in water at 25°C of 5 or higher, c) a molar ratio of 1,3,5-triazine compound to phosphorus (M/P)&#8804;1.1, and d) a decomposition temperature > 320° C, at which the loss of weight amounted to 2%, e) a solubility&#8804;0.1 g/100 ml.

Full Text

Polyphosphate derivative of a 1,3,5-triazine compound, a process
for the production thereof and use thereof
WO 00/02869 discloses polyphosphate salts of 1,3,5-triazine
compounds which have an average condensation coefficient (number
average) of greater than 20 and a molar ratio of triazine compound such as
melamine to phosphorus (M/P) > 1.1. The WO-specification also describes
a two-stage process for the production of those salts by conversion of a
1,3,5-triazine compound with orthophosphoric acid into the corresponding
orthophosphate salt as well as thermal treatment for conversion of the
orthophosphate salt into a polyphosphate of the 1,3,5-triazine compound.
In addition to the orthophosphates it is also possible to use
pyrophosphates. The polyphosphate salts described in that publication are
desirably to be used as flame-retardant agents.
WO-specification WO 97/44377 describes a melamine
polymetaphosphate of a solubility of 0.01 to 0.10 g/100 ml in water at
25°C, a pH-value of 2.5 to 4.5, in the form of a 10% aqueous slurry at
25°C and a melamine content of 1.0 to 1.1 mole per mole of phosphorus.
That melamine polymetaphosphate is also obtained in a two-stage process
in which in a first stage melamine, urea and an aqueous orthophosphoric
acid solution are mixed together in such a ratio that the molar ratio of
melamine to orthophosphoric acid is 1.0 to 1.5 and the molar ratio of urea
to orthophosphoric acid is 0.1 to 1.5. The reaction is effected at a
temperature of 0 to 140°C with the removal of water, a powder double salt
of orthophosphoric acid, melamine and urea being obtained. In a second
stage that is calcined at a temperature of 240 to 340°C and in that case
affords melamine polymetaphosphates. That publication also refers to

flame-retardant agents as the field of use for the melamine
polymetaphosphates.
WO 00/02869 refers to the disadvantage of the melamine
polymetaphosphates in accordance with WO 97/44377 that the melamine
polymetaphosphates produced in accordance with the process described
therein are unsuitable for the use as flame-retardant agents in polymers, in
particular in polyamides and polyesters which are typically processed at
elevated temperatures. According to the information set out in WO
00/02869 those melamine polymetaphosphates have inadequate heat
resistance, impact strength, tensile strength and breaking strength. There
was therefore no reason for the man skilled in the art to find pointers in
WO 97/44377 for example for improving the polyphosphate salts in
accordance with WO 00/02869.
European laid-open application No 1 386 942 discloses flame-
retardant agents which include a phosphinate or diphosphinate together
with a 1,3,5-triazine compound, which are intended to improve the effect
over the individual substances.
When using polyphosphate salts in accordance with WO 00/02869 as
flame-retardant agents in plastic materials, in particular in glass fibre-
reinforced polyamides, polyesters, such as polyethylene terephthalate and
polybutylene terephthalate which are usually processed at relatively high
temperatures (more specifically above 320°C), premature partial
decomposition was also noted, which on the one hand lead to an attack by
the decomposition products on the moulding tools used and which later
when used for example as electrical insulating lacquers on copper wires
lead to an attack on the latter.
The object of the invention was therefore that of further improving
the polyphosphate salts of 1,3,5-triazine compounds, which are known
from WO 00/02869, so that they are heat-resistant even at processing
temperatures above 320°C and for that purpose have a low level of water
solubility and a low level of conductivity. Surprisingly that object was
attained by the present invention, in respect of which information on page
2 and page 11 of WO 00/02869 is in part in conflict. The polyphosphate

derivatives according to the invention of a 1,3,5-triazine compound, in
particular melamine polyphosphate, with an average condensation
coefficient n (number average) > 20 and a pH-value of a 10% aqueous
slurry of the polyphosphate derivative at 25°C of 5 or higher are
characterised in that they have a molar ratio of 1,3,5-triazine compound to
phosphorus, M/P 320°C.
Those polyphosphate derivatives can be used as flame-retardant
agents in any plastic materials, preferably thermoplastic materials and
thermosetting materials, in particular also in glass fibre-reinforced
polyamides and polyesters which are processed at high temperatures. In
consideration of the information in WO 00/02869 on pages 1 and 2 as well
as page 11, lines 15 - 20, that result was not to be expected but rather the
man skilled in the art had to reckon on the fact that, with a M/P
pH-value of the melamine polyphosphate above 5 can be obtained and that
the phosphate derivatives with such a low M/P are not suitable as a flame-
retardant agent for plastic materials such as glass fibre-reinforced
polyamides and polyesters, because of the excessively low level of heat
resistance.
Because of the surprising heat resistance of the polyphosphate
derivatives according to the invention, there are no longer any limitations
in terms of the use of melamine polyphosphates and corresponding triazine
derivatives as flame-retardant agents in plastic materials, in particular
thermoplastic materials. The series of plastic materials into which the
polyphosphate derivatives according to the invention can be incorporated
are to be found on pages 6 and 7 of WO 00/02869, and for that reason the
content of those pages is hereby made the subject-matter of the present
application.
The polyphosphates of the invention can be reproduced in simplified
form by the following general formula:

wherein M denotes a 1,3,5-triazine compound and n denotes the average
condensation coefficient. For high and medium condensation coefficients
n the sum formula can be reduced to (MHP03)n. Therein M once again
denotes the 1,3,5-triazine compound and n denotes the average
condensation coefficient.
1,3,5-Triazine compounds which fall to be considered are for
example 2,4,6-triamine-l,3,5-triazine (melamine) and its derivatives,
condensation products such as melam, melem, melon, ammeline and
ammelide but also 2-ureidomelamine, acetoguanamine, benzoguanamine
and diaminophenyltriazine. It will be appreciated that it is also possible to
use mixtures of those 1,3,5-triazine compounds. Melamine, its derivatives
and condensation products are preferred in the present invention, in
particular melamine.
The average condensation coefficient n of the phosphates can be
ascertained in accordance with known methods such as for example by
means of NMR, J. Am. Chein. Soc. 78, 5715 (1956). The average
condensation coefficient n is preferably at least 30, still more preferably in
the range of 40 to 150. That average condensation coefficient can also be
referred to as the average chain length of the phosphate derivative.
The polyphosphate derivatives according to the invention have an
enhanced heat resistance at 320° to 370°C. That is determined by the
temperature at which the weight loss is 2%. The low M/P-ratio results in a
higher P content and thus a process effect which is 15% better and an
extremely low level of water solubility, which is of very great significance in
terms of plastic products, in particular in the outdoor region. The water
solubility of the polyphosphate derivatives according to the invention is
preferably below 0.1 g/100 ml and still more preferably below 0.01 g/100

ml. With those orders of magnitude it is possible to refer to a product which
is virtually insoluble in water.
As mentioned the molar ratio M/P is preferably below 1.0 and still
more preferably between 0.8 and 1.0.
The pH-value is determined in a 10% aqueous slurry of the
polyphosphate derivative according to the invention, by a procedure
whereby 25g of the polyphosphate derivative and 225g of pure water are
stirred at 25°C in a vessel and the pH-value of the resulting aqueous
suspension is determined with conventional means. Preferred pH-values
are approximately in the range of 5.1 to 6.9.
Preferably the polyphosphate derivatives according to the invention
have a decomposition temperature above 360, particularly above 380 and
in particular above 400°C.
A process according to the invention for the production of the
polyphosphate derivatives set forth in claims 1 to 6 provides that an
orthophosphate and/or at least one condensed phosphate of a 1,3,5-
triazine compound, preferably melamine, with an average condensation
coefficient n of below 20, is heat-treated in an ammonia atmosphere at a
temperature in the range of 300 to 400°C, preferably in the range of 340 to
380°C, particularly preferably in the range of 370 to 380°C, and in that
case a condensation product with an average condensation coefficient n
(number average) > 20 is obtained.
Usually the starting material involved is the melamine
orthophosphate but that can be supplemented or replaced by condensed
phosphates such as for example pyrophosphates and less condensed
polyphosphates. The heat treatment must be effected for different periods
of time at different temperatures depending on the respective starting
phosphate used so that at any event the average condensation coefficient
is above 20. The concentration of the ammonia in the gas atmosphere of
the heat-treatment zone is desirably in the range of 0.1 to 100% by mass,
preferably in the range of 1 to 30%, particularly in the range of 2 to 10%,
in particular 3 to 5%. It is particularly desirable for the starting material
used to be a 1,3,5-triazine compound, preferably a melamine compound,

with a particle size which is as fine as possible, desirably an average
particle size≤15 urn, preferably≤10 urn. With a coarser particle size
grinding of the starting products is desirably effected prior to the heat
treatment in order to produce the specified average particle sizes ≤ 15 µm,
preferably ≤ 10 µrn.
The flame-retardant properties of the polyphosphate derivatives
according to the invention of a 1,3,5-triazine compound can be further
increased if the polyphosphate derivatives are combined with at least one
phosphinate and/or diphosphinate.
Preferably the phosphinates or diphosphinates are of the following
formulae I and II respectively:

x is 1 - 4.
Particularly preferably M is the same as Al. Desirably the flame-
retardant mixtures contain so much of the polyphosphate derivative (A)
according to the invention and the diphosphinate (B) that A:B = 3:7 to 7:3,
preferably 3:4 to 4:3.
The flame-retardant properties of the polyphosphate derivatives
according to the invention of a 1,3,5-triazine compound can be quite
particularly preferably also increased by the polyphosphate derivatives
being mixed with aluminium phosphinates of the general formula (I):

wherein
R1 is -CH3, -CH2OH, -C2H5, -CH(OH)CH3 or -C(OH)(CH3)2,
R2 is -CH2OH, -C2H4OH, -C3H6OH or -CH(OH)CH3,
M is Al, and
m 1 to 4
The aluminium phosphinate mixtures can be obtained by the free
phosphinic acids being obtained in aqueous solution in known manner from
alkali phosphinate mixtures and by their being reacted by subsequent
boiling with aluminium hydroxide or aluminium oxyhydroxide slurries in
water. It is found however that this neutralisation reaction takes up
reaction times which are many times longer. It is therefore more
appropriate for the alkali phosphinates obtained from the phosphorus
reaction to be caused to react with the required amount of water-soluble
aluminium salts such as for example chloride, hydroxychloride, sulphate,
nitrate or formiate in aqueous solution, in which respect it may be
necessary to completely dissolve the mixture by a small mineral acid
addition and then to precipitate the aluminium phosphinate mixtures by
raising the pH-value to 4 to 7. Subsequent heating of the aqueous
suspension to temperatures between 105 and 150°C in pressure vessels

facilitates later separation of the difficultly soluble precipitate. The
aluminium phosphinate precipitate is then filtered, washed and dried.
A further advantageous embodiment of the invention is characterised
in that all or a part of the flame-retardant agents, that is to say the
polyphosphinate derivative or derivatives and/or the phosphinate or
phosphinates and/or diphosphinate or diphosphinates and/or the further
included per se known flame-retardant agents, are coated with a silicon-
bearing coating agent and/or modified in some other fashion. Such a
modification is known for example from DE 198 30 128 Al, the content of
which is hereby incorporated into the subject-matter of the present
application by reference thereto. With the modification procedure an
organofunctional silane or a mixture of organofunctional silanes or an
oligomeric organosiloxane or a mixture of oligomeric organosiloxanes or a
solvent-bearing preparation based on monomeric organosilanes and/or
oligomeric organosiloxanes or a preparation based on water-soluble
organopolysiloxanes are applied to a flame-retardant agent in powder form
and the flame-retardant agent is kept in motion during the coating
operation.
Preferably 0.05 to 10% by weight of silicon-bearing coating agent
with respect to the amount of flame-retardant agent is used. Desirably the
coating agent is applied to the flame-retardant agent in the course of 10
seconds to 2 hours at a temperature of 0 to 200°C. It is further
advantageous if the flame-retardant agent which is coated with coating
agent is subjected to a post-treatment under the effect of heat at a
temperature of up to 200°C and/or under reduced pressure. The
organofunctional silane used is advantageously an aminoalkyl- or
epoxyalkyl- or acryloxyalkyl- or methacryloxyalkyl- or mercaptoalkyl- or
alkenyl- or alkyl-functional alkoxysilane.
A particular advantage of modifying the flame-retardant agent with
silicon-bearing coating agent is that the flame-retardant agent is more
resistant to environmental influences such as moisture. The modification
provides that washing-out of the flame-retardant agent in the course of
time is prevented or reduced.

The invention is further described by reference to the following
Examples.
Example 1 and Comparative Example 1
a. 876.96 kg of melamine was mixed in a blade mixer. 784 kg of
75% phosphoric acid was brought into contact with the melamine by
spraying, in which case the reaction took place. The melamine
orthophosphate formed was finely ground in an ACM-mill.
b. The melamine orthophosphate was heat-treated in an oven.
The oven temperature was set to 380°C before the melamine
orthophosphate was introduced into the oven. The temperature and
the ammonia concentration in the oven atmosphere were
respectively set and kept approximately constant throughout the
entire experiment. An ammonia atmosphere was created in the oven,
with the ammonia concentration in the ammonia atmosphere being
variable.
In Example 1 in accordance with the invention a relatively high
ammonia concentration, namely corresponding to -3 mm water column,
was set. One result was that the pH-value was 5.524 and thus markedly
above 5. At the same time the solubility at 0.032 g/100 ml was reduced to
approximately a third in comparison with the subsequent Comparative
Example. It was not possible to find any chemical attack on the moulding
tools in the subsequent processing operation. The heat resistance of the
product of Example 1 was about 373°C-TGA (2% weight loss), that is to
say a weight loss of 2% was achieved at about 373°C.
In Comparative Example 1 a lower ammonia concentration than in
Example 1 was set by altering the level of ammonia concentration in the
oven atmosphere. That corresponded to -100 mm water column. The effect
was that the pH-value now abruptly fell and was about 3.57 in the
suspension. The heat resistance was about 353°C-TGA (2% weight loss).
The conditions and results of this experiment are set out in Table 1.

In this case the heat resistance was practically the same in both
tests, but the pH-value in Example 2 according to the invention is
considerably higher than in the case of Comparative Example 2.

WE CLAIM:
1. A polyphosphate derivative of a 1, 3, 5-triazine compound, preferably melamine
polyphosphate, with
a) an average condensation coefficient n (number average) > 20,
b) with a pH-value of a 10% slurry of the polyphosphate derivative in water at
25°C of 5 or higher,
c) a molar ratio of 1,3,5-triazine compound to phosphorus (M/P)≤1.1, and
d) a decomposition temperature > 320° C, at which the loss of weight amounted
to 2%,
e) a solubility≤0.1 g/100 ml.
2. A polyphosphate derivative as claimed in claim 1, wherein
e) it has a solubility≤0.01 g/100 ml.
3. A polyphosphate derivative as claimed in claim 1 or 2, wherein it has a molar ratio
(c) of 1,3,5-triazine compound to phosphorus
between 0.8 und 1.0.
4. A polyphosphate derivative as claimed in one of claims 1 to 3 wherein a 10%
slurry of the polyphosphate derivative in water at 25° C (b) has a pH-value in the
range of 5.1 to 6.9.
5. A polyphosphate derivative as claimed in one of claims 1 to 4, wherein
a) its average condensation coefficient (number average) > 30, particularly from
40 to 150.

6. A polyphosphate derivative as claimed in one of claims 1 to 5 wherein
d) its decomposition temperature is higher than 360°C, preferably higher than
380°C, particularly higher than 400° C.
7. A process for the production of a polyphosphate derivative of a 1, 3,5-triazine
compound as claimed in one of claims 1 to 6, wherein an orthophosphate or a
condensed phosphate of a 1,3,5-triazine compound with an average
condensation coefficient n (number average) below 20 is heat-treated in an
ammonia atmosphere at a temperature in the range of 300 to 400°C until the
average condensation coefficient is above 20 and the molar ratio of 1,3,5-
triazine compound to phosphorus (M/P) is below 1.1.
8. A process as claimed in claim 7 wherein the heat treatment is effected in a
temperature range of 340 to 380, preferably 370 to 380°C.
9. A process as claimed in claim 7 or 8 wherein prior to the heat treatment the
polyphosphate derivative is ground to an average particle size ≤15 µm,
preferably 10 µm.
10. A process as claimed in one of claims 7 to 9 wherein the heat treatment is
effected in an ammonia atmosphere which contains ammonia in a concentration
of 0.1 to 100, preferably 1 to 30, particularly 2 to 10, in particular 3 to 5% by
mass.

11. A flame-retardant agent including at least one polyphosphate derivative of a
1,3,5-triazine compound as claimed in one of claims 1 to 6.
12. A flame-retardant agent as claimed in claim 11 wherein it also contains other per
se known flame-retardant agents.
13. A flame-retardant agent as claimed in one of claims 11 and 12 wherein it
additionally contains at least one phosphinate and/or diphosphinate.
14 A flame-retardant agent as claimed in one of claims 11 to 13 wherein it contains
phosphinate of the general formula I and/or diphosphinate of the general
formula II:

wherein
R1, R2 are the same or different and C1-C6-alkyl, straight or branched, C1-C7-
hydroxyalkyl, straight or branched, or aryl,
R3 is C1-C10-alkyls, straight or branched, C6-C10-aryls, alkylaryls or
arylalkyls,
M is Mg, Ca, Al, Sb, Sn, Ge, Ti, Zn, Fe, Zr, Ce, Bi, Sr, Mn, Li, Na, K and/or
a protonised nitrogen base, preferably Ca, Mg, Al and Zn,
m is 1 to 4,
n is 1 to 4, and
x is 1 -4.
15. A flame-retardant agent as claimed in claim 14 wherein M = Al.
\6, A flame-retardant agent as claimed in claim 14 wherein the phosphinate is a
phosphinate of the general formula I:

wherein
R1 is -CH3, -CH2OH, -C2H5, -CH(OH)CH3 or -C(OH)(CH3)2,
R2 is -CH2OH, -C2H4OH, -C3H6OH or -CH(OH)CH3.
M is Al, and
m 1 to 4
A flame-retardant agent as claimed in one of claims 11 to 16 wherein the
polyphosphate derivative or derivatives and/or the phosphinate or phosphinates
and/or diphosphinate or diphosphinates and/or the further included per se
known flame-retardant agents are coated with a silicon-bearing coating agent
and-or modified in some other fashion.

A polyphosphate derivative of a 1, 3, 5-triazine compound, preferably melamine
polyphosphate, with a) an average condensation coefficient n (number average)
> 20, b) with a pH-value of a 10% slurry of the polyphosphate derivative in water
at 25°C of 5 or higher, c) a molar ratio of 1,3,5-triazine compound to phosphorus
(M/P)≤1.1, and d) a decomposition temperature > 320° C, at which the loss of
weight amounted to 2%, e) a solubility≤0.1 g/100 ml.